MEIOSIS

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MEIOSIS

• Making Sex Cells

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Get the Lingo Down!!!

• Somatic cell body cell

Skin Nerve
Blood
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Human Chromosomes

• How many chromosomes?
• 46
• How many pairs of chromosomes?
• 23

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Homologous Chromosomes

• Two sister chromatids joined at the centromere
  From MOTHER plus
• Two sister chromatids joined at the centromere
  From FATHER
• All Four Chromatids carrying genes controlling
  the same inherited characteristics

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Loci

• The place on a chromosome where a specific gene
  is located
• The plural is "loci," not "locuses."
• EXAMPLE gene for hair color
• Gene for height

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Autosomes

• Any chromosome that is not a sex chromosome
• Humans - 1 through 22

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Sex Chromosomes

• Female XX
• Male XY
• Chromosome 23
• Is this a male or female?

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Is this a male or female?
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Where do we get the pair of chromosomes?

• One set from our father
• One set from our mother

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Human Cells

• Diploid number
• 2n
• 46
• somatic cells

• Haploid number
• n
• 23
• sex cells

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Sex Cells

• Gametes
• EX Egg and Sperm

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Are Gametes n or 2n?

• N
• Single set of chromosomes

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Are Gametes haploid or diploid?

• -Haploid 23
• -n

23 chromosomes
egg
23
sperm
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Fertilization

• Fusing of Egg and Sperm
• Woo-Hoo!
• Whats the
• Fertilized egg called?
• Zygote

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Where are the sex cells made?

• Testes make sperm
• Ovaries make eggs

Only in reproductive organs
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What is the process

• In which sex cells are made?
• MEIOSIS

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How many cells formed?Haploid or Diploid?
4 haploid 2 diploid
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MEIOSIS INTERPHASE

• Yes, the chromosomes duplicate
• Still chromatin, loose

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Meiosis I Prophase I
90 of meiosis time
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Meiosis I Prophase I
Synapsis formation of a tetrad (4 homologous
chromosomes)
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Lets Review All DNA and Protein
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With Jonathan Edwardswhatever happened to him,
anyway?
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Lets See a Close-up Crossing Over
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Chiasma

• Sites of crossing over
• Appear as X-shaped regions
• Site where two
  homologous
  chromosomes are
  attached to
  each
  other

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Genetic Recombination

• The production of
  gene combinations
  
  different from those
  carried by the
  original
  chromosomes
• ADVANTAGE increases diversity

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What else happens Prophase I?

• What dissolves?
• Nuclear Membrane and Nucleolus

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What else happens Prophase I?

• What also forms?
• spindles

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Meiosis I Metaphase I
Where are the tetrads lined up?Metaphase plate
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Meiosis I Anaphase I
Where are the sister chromatids going? Apart to
the poles NOTE the double strands
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Meiosis I Telophase I
Note the double strands at the poles Cytokinesis
begins
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Interkinesis/Cytokinesis

• Some cells will go into a temporary
  chromatin-forming interphase (like in humans)
  called interkinesis

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Interkinesis/Cytokinesis

• Some will immediately go into Prophase II
• NOT ALL CELLS DO THIS AT THE SAME TIMEBUT ALL
  WILL EVENTUALLY GO INTO PROPHASE II

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Interkinesis/Cytokinesis

• (Different than mitosis interphase, however)
• NO NEW DUPLICATION OF CHROMOSOMES
• FURTHER DIVISION OF THE CHROMOSOMES WILL OCCUR

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Meiosis II Prophase II
How many cells are there? 2 What is
dissolving? Nuclear membrane Whats forming?New
spindles
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Meiosis II Metaphase II
How many cells? 2 Where are the chromatids lined
up?Metaphase (equatorial plate)
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Meiosis II Anaphase II
How many cells? 2 What are the single chromosomes
doing?Moving to poles
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Meiosis IITelophase II
How many cells will result at the end? 4 Will the
cells be haploid or diploid?Haploid
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Name the Phase (Meiosis I)
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Name the Phase (Meiosis II)
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Sperm MeiosisAll cells same size
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Sperm maturing in a seminiferous tubule
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Egg MeiosisOne large egg, 3 small polar bodies

• oogenesis

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Follicle and egg
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Contrast

• MITOSIS
• 1 division
• (PMAT)
• Results in 2 daughter cells

• MEIOSIS
• 2 divisions
• (PMAT) I and (PMAT) II
• Results in 4 daughter cells

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Contrast

• MITOSIS
• Diploid offspring
• Makes somatic cells

• MEIOSIS
• Haploid offspring
• Makes sex cells

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Contrast

• MITOSIS
• Makes identical cells
• Same number of chromosomes

• MEIOSIS
• Makes similar cells
• Half the number of chromosomes

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Independent Assortment

• This means that traits are transmitted to
  offspring independently of one another.
• Independent Assortment Animation

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Independent Assortment

• In other words,
• RANDOM COMBINATION OF ALLELES APPEAR IN THE
  GAMETES

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How many possible combinations are there?

• 2n
• n haploid number
• 22 ?
• 8

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How many combos?

• When one man (223) combines with one woman (223)?
• 246

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How many combos from independent assortment

• HUMANS
• 223 ?
• About 8 million
• (8,388,608)

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If only one crossover occurs, how many possible
combinations?

• 423 combinations
• (70,368,744,000,000)

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With fertilization and crossing-over, how many
combos possible?

• (4 23) 2 4,951,760,200,000,000,000,000,000,000

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Wait a second

• What are alleles?

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Alleles

• Different Versions of Genes
• FOR EXAMPLE B brown eye color
  b blue eye
  color
• FOR EXAMPLE T Tall
• t short

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More Allele Examples (fruit)

• Hi Hard rind inhibitor
• Hr Hard rind
• l light fruit color
• Rd dominant Red skin color of fruit
• St stripped fruit lengthwise

Rd dominant Red skin color of fruit
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Dog Breeds Lots of Alleles
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Dog Color Alleles

• in order of decreasing dominance
• Ay - agouti "red" (black, if any, appears in
  restricted areas only)Aw - "white-bellied"
  agouti
• A - solid agouti at - black tana non agouti
  (recessive black)
• Ea - dominant black
• Em - black mask

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Why are the cells formed in meiosis different
from the parents?

• Random Fertilization (who ya have sex with)
• Independent Assortment
• Crossing Over

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So an advantage of Meiosis

• A tremendous amount of genetic variation is
  possible!

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Lets Review

• Three sources of genetic variability
• 1. Crossing over during prophase I of meiosis
• 2. Independent orientation of chromosomes at
  metaphase I
• 3. Random fertilization

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Karyotype

• An orderly display of magnified images of the
  individuals chromosomes
• Shows the
  chromosomes as
  they appear in
  metaphase

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What is a Normal Karyotype?

• We are supposed to have 46 total chromosomes in
  each cell (22 pairs of autosomes 44, 2 sex
  chromosomes).

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Preparing a Karyotype

• 1. Use lymphocytes (white blood cells)
• 2. Chemical to stimulate division
• 3. Chemical to stop in metaphase
• (stop spindle fibers
  forming)

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Preparing a Karyotype (cont)

• 4. Centrifuged to remove white blood cells
• 5. Chromosomes spread out in hypotonic solution.
• 6. Drop on a slide.
• 7.Sort by size and shape.

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Resulting Photograph

• Sort by size and shape
• Largest to smallest

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Amniocentesis

• Take fluid from amniotic fluid around the baby

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Spectral Karyotype
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Normal Karyotype

• WHY?

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Down Syndrome Karyotype

• Trisomy 21

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Down Syndrome

• Trisomy 21
• Folds over eyes
• Sluggish muscles
• Mental Problems

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Down Syndrome

• The most common
  chromosome number
  abnormality
• Round face
• flattened nose bridge
• small, irregular teeth

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Down Syndrome

• Short Stature
• heart defects
• susceptibility to
  respiratory infection ,
  leukemia and
  Alzheimers

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Does the mothers age matter?

• As the age of the mother increases above 30, the
  frequency of Trisomy 21 also increases

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Abnormal Sex Chromosomes

• 47 XXY syndrome
• male
• testes small (sterile)
• breast enlargement
• feminine body contours
• also XXYY, XXXY, XXXXY

• Klinefelters

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TURNER SYNDROME

• XO (only one X)
• short
• often web of skin between neck and shoulders
• sterile
• poor breast development

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Turner Karyotype
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Why are the cells formed in meiosis different
from the parents?

• Random Fertilization (who ya have sex with)
• Independent Assortment
• Crossing Over

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How many possible combinations are there?

• 2n
• n haploid number
• 22 ?
• 8

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DELETION
Fragment of the chromosome is lost
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Duplication
Fragment of one chromosome attaches to a
homologous chromosome
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Translocation
Fragment reattaches in reverse direction (less
likely to produce harm)
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INVERSION

• The chromosome breaks in two places, a piece of
  the chromosome is removed and the chromosome
  pieces remaining rejoin.
• Less likely to remove harm

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INVERSION 46,XY,inv(16)

• The left one is normal and the right one is
  inverted near the centromere.Inversions, by
  definition, do not involve loss or gain of
  chromosomal material.

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45,XX,rob(13,14) A Robertsonian translocation
(an end to end fusion of 13 and 14 There is no
net gain or loss of genetic material
in
this person so they would
have a normal

phenotype.
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Locus
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Broccoli Cauliflower Broccoflower
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Male Lion X Female Tiger

• Liger

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